This invention pertains to bone surgery. Specifically, the invention is directed to instrumentation and methods for preparing adjacent bones for receiving an implant therebetween. The invention is particularly advantageous for preparing an implant site for fusing vertebral bodies to facilitate fusion.
Chronic back problems can cause pain and disability for a large segment of the population. Frequently, the cause of back pain is traceable to diseased disc material between opposing vertebrae. When the disc material is diseased, the opposing vertebrae may be inadequately supported, resulting in persistent pain.
Surgical techniques have been developed to remove the diseased disc material and fuse the joint between opposing vertebral bodies. Arthrodesis or fusion of the intervertebral joint can reduce the pain associated with movement of an intervertebral joint having diseased disc material. Generally, fusion techniques involve removal of the diseased disc and inserting a bone or non-bone implant between the opposing vertebral bodies to be fused.
Spinal fusion implants and related surgical instruments for implanting a fusion device are known and disclosed in, for example, U.S. Pat. Nos. 5,741,253; 5,722,977; 5,658,337; 5,609,636; 5,505,732; 5,489,308; 5,489,307; 5,458,638; 5,055,104; 5,026,373; 5,015,247; 4,961,740; 4,878,915; 4,834,757; 4,743,256; 4,501,269; and 3,848,601. The disclosure of each of these patents is incorporated herein by reference.
Often times, the degenerative changes of the diseased disc cause a collapse of the intervertebral disc space. Thus, prior to implantation, the intervertebral disc space may be distracted to restore the normal height of the disc space or the normal relationship between the vertebrae to be fused. Maintaining the restored disc space height and/or vertebral relationships throughout preparation of the implant site can be important for the ultimate stability at the fusion site.
The ease of use and efficiency of instruments and procedures used to prepare and place an implant at a fusion site is also very important to the overall success of the procedure. For example, in addition to other problems, removal of unequal amounts of bone on either side of the fusion site, particularly in vertebral fusion procedures, can result in over reaming of one vertebra relative to the adjacent vertebra and ultimately lead to a poorer surgical outcome.
Accordingly, there is a continuing need for instrumentation and methods that ensure precise placement of the implant as well as increasing the ease and efficiency of the implant procedure. The present invention is directed to this need.
The present invention is directed to bone cutting instruments and methods that provide efficient and precise preparation of a bore for receiving an implant between adjacent bones that are to be fused.
Throughout the specification, guidance may be provided through lists of examples. In each instance, the recited list serves only as a representative group. It is not meant, however, that the list is exclusive.
In one embodiment, the instruments of the invention include bone cutting instruments having paddles that can be inserted between adjacent bones to maintain a fixed spacing between the bones during preparation of the bones for fusion. In one embodiment, the bone cutting instruments include a cutting edge that is fixedly mounted to the spacing paddles. In an alternative embodiment, the paddles can be mounted to a channel guide that provides a track for slidably positioning the cutting edge at the site of bone preparation.
In a typical embodiment, a bone cutting instrument includes a cutting edge that extends beyond the height dimensions of the paddles with a portion of the cutting edge extending between the paddles. Depending on the configuration of the implant to be inserted between bones, the cutting edge can be circular, oval, rectangular, etc.
In another embodiment, a bone cutting instrument includes first, second, third, and fourth cutting edges that define an interior void, with the first and second cutting edges being opposite and extending beyond the third and fourth cutting edges.
In a further embodiment, the invention involves a rasp adapted to define a recess between two bone surfaces. The rasp includes a shaft and a rasp head with an arcuate distal surface. At least one of the transverse surfaces of the rasp is roughened. Examples of roughened surfaces include knurls, etchings, ridges, grooves, teeth, etc.
In a still further embodiment, the invention involves an implant insertion tool having a shaft with a pair of arms movable between a spaced apart holding position and a close together releasing position. The distal ends of the arms are shaped to fit inside an implant. The insertion tool also involves a sleeve operable on the arms to force the arms together towards the releasing position. The sleeve is hollow and is slidably mounted on the shaft. The sleeve forces the arms together to release the implant when the sleeve is in the engaging position. In an alternative embodiment, the sleeve is internally threaded and the shaft is externally threaded, with the threads matching. In this embodiment, the sleeve is rotated to move it along the shaft. The invention also provides kits comprising one or more instruments of the invention having various paddle and/or cutting edge heights, widths or shapes for preparing an implant site of a predetermined size or shape.